Tumor PD-L1 Expression Research Articles

A protocol pre-specified interim overall survival (OS) analysis of GEMSTONE-302: A phase 3 study of sugemalimab (suge) versus placebo plus platinum-based chemotherapy (chemo) as first-line (1L) treatment for patients (pts) with metastatic non–small cell lung cancer (NSCLC).

9027 Background: GEMSTONE-302, a randomized, double-blind, phase 3 study, previously met its primary endpoint and demonstrated statistically significant and clinically meaningful prolongation of progression-free survival (PFS) with suge+chemo vs placebo+chemo as a 1L treatment in pts with metastatic NSCLC. PFS benefit was observed in both squamous (sq) and non-squamous (nsq) NSCLC, regardless of PD-L1 expression levels. Here we report the data from a protocol pre-specified interim OS analysis. Methods: Pts with systemic treatment-naïve stage IV NSCLC, measurable disease per RECIST v1.1, ECOG PS 0-1, and no known EGFR, ALK, ROS1 and RET alterations were randomized 2:1 to receive suge (1200 mg, IV) or placebo plus chemo (sq-NSCLC: carboplatin+paclitaxel; nsq-NSCLC: carboplatin+pemetrexed) every 3 weeks for up to 4 cycles, followed by maintenance therapy (sq-NSCLC: suge/placebo; nsq-NSCLC: suge/placebo+pemetrexed) for up to 35 cycles. The primary endpoint was investigator assessed PFS (INV-PFS). Key secondary endpoints included OS, INV-PFS in pts with tumor PD-L1 expression ≥1%, and ORR. Pts in the placebo group could cross over to receive suge monotherapy upon disease progression. Results: As of 22 Nov 2021, among all 479 enrolled pts, 51 (15.9%) and 7 (4.4%), respectively, remained on treatment with suge+chemo or placebo+chemo. The median follow-up was 25.4 and 24.9 months, respectively. Following treatment discontinuation, 17.8% and 43.4% of the pts, respectively, received cross-over suge or other non-study anti-PD-(L)1-containing therapies. Median OS was 25.4 months in suge+chemo group vs 16.9 months in placebo+chemo group (HR = 0.65 [95%CI, 0.50-0.84], p = 0.0008), and 2-year OS rate was 51.7% vs 35.6%. OS benefits were observed across all subgroups including different tumor histologies (sq: HR = 0.56; nsq: HR = 0.72) and PD-L1 expression levels (≥1%: HR = 0.64; < 1%: HR = 0.66). In the intent-to-treat population, median PFS was 9.0 months with suge+chemo vs 4.9 months with placebo+chemo (HR = 0.49 [0.40-0.61]), and 2-year PFS rate was 20.8% vs 7.3%. In pts with PD-L1≥1%, the median PFS was 10.9 vs 4.9 months (HR = 0.48 [0.36-0.63], p < 0.0001). ORR was 63.4% vs 40.3% (p < 0.0001). Among pts with baseline brain metastases, suge+chemo improved their OS (HR = 0.45) and intracranial INV-PFS (post-hoc analysis, HR = 0.33) vs placebo+chemo. Safety profile was consistent with previously reported results. Conclusions: Suge plus chemo demonstrated statistically significant and clinically meaningful OS improvement compared with placebo plus chemo, irrespective of tumor histology or PD-L1 expression levels, in pts with newly diagnosed metastatic NSCLC, offering a new 1L treatment option for this group of pts. Clinical trial information: NCT03789604.

Impact of HIV infection on clinical outcomes among people diagnosed with head and neck cancer.

e18080 Background: Incidence of non-AIDS-defining cancers, including head and neck cancer (HNC), is rising among people with HIV (PWH) in the combination antiretroviral therapy (cART) era. The following study compares demographics, clinical outcomes, and the tumor microenvironment of HIV+ and Uninfected HNC patients at a single institution. Methods: Yale Tumor Registry query identified 3,356 HNC patients from 2002 to 2018 for analysis, including 50 PWH. In addition, quantitative immunofluorescence (QIF) was performed on tumor tissue from 22 PWH and 75 matched Uninfected patients. HPV status was based on p16 staining done universally among oropharyngeal squamous cell carcinomas (OPSCC) after 2010. Results: PWH were younger at cancer presentation compared to Uninfected patients (55.5 vs. 62.0, p < 0.001), with differences in race/ethnicity and insurance status (p < 0.001 for both). Biologic sex, tobacco use, alcohol consumption, anatomic site, stage at presentation, stage-specific treatment, and time to initiation of treatment were comparable between HIV+ and Uninfected cohorts. 89% of the PWH were on cART, with 79% achieving viral loads ≤200 copies/mL and a median CD4 count of 341 cells/mm³. Median survival among PWH was 39.1 months, compared to 100.8 months among Uninfected patients (p < 0.001). In a multivariate (MV) analysis that included age, sex, race/ethnicity, tobacco use, anatomic site, stage, time to treatment initiation and insurance status, HIV was an independent predictor of poor outcome (HR 1.88 with 95% CI: 1.25-2.81). Difference in survival was noted particularly in early stage (stages 0, I, II) cancer, with a median survival of 73.8 months in PWH compared to 141.9 months in Uninfected patients (p = 0.001). Survival was comparable among late stage (stages III, IV) HNC patients. Among PWH, increased HIV viral load was associated with poor outcome in a MV analysis (p = 0.03). Among HPV-associated OPSCC, PWH had decreased survival compared to Uninfected patients (p < 0.001). In our study of the tumor microenvironment by QIF, tumors of PWH had lower tumoral CD8 T cell infiltration (p = 0.04) and lower PD-L1 expression in tumor, stroma, and combined compartments (CPS) (p = 0.01, p = 0.03, and p = 0.01, respectively) compared to Uninfected patients. Conclusions: In our single institution study, HNC patients living with HIV experienced decreased overall survival, with HIV serving as an independent predictor of poor outcome in a multivariate analysis which included insurance status and treatment approaches. Difference in outcome was significant among early stage tumors and among HPV+ OPSCC. CD8 T cell infiltration and PD-L1 expression, both associated with improved outcomes in the general population, are decreased within the TME of PWH. Our data suggest that HIV-associated HNC is associated with poorer outcomes and highlight differences in tumor biology that require further detailed characterization in large cohorts.

P-49 GOBLET: A phase 1/2 multiple indication signal finding and biomarker study in advanced gastrointestinal cancers treated with pelareorep and atezolizumab – safety and preliminary response results

In GI cancers, checkpoint inhibitors are only effective in patients with high microsatellite instability (MSI-H) or deficient mismatch repair (dMMR) tumors. Oncolytic viruses may improve the susceptibility of microsatellite stable (MSS) tumors to immunotherapy by modifying the tumor microenvironment (TME). Pelareorep (pela) is an intravenously delivered, non-genetically modified, oncolytic reovirus that mediates cancer cell killing by activating innate and adaptive immune responses directed against the tumor as well as direct tumor oncolysis. Accordingly, treatment with pelareorep results in increased T cell infiltration and PD-L1 expression in tumors which primes the TME for responsiveness to checkpoint inhibitors. Pela has demonstrated activity in many cancers including colorectal and pancreatic cancer. The GOBLET study is designed to assess the efficacy of pela plus atezolizumab (atezo) with or without chemotherapy in multiple GI cancers. GOBLET is a phase 1/2, open-label, non-randomized study in patients with advanced or metastatic GI cancers and utilizes a Simon two-stage design. In the first stage of the study, four treatment groups are being enrolled: Cohort 1 – First-line metastatic/advanced pancreatic cancer treated with pela plus atezo and chemotherapy (gemcitabine and nab-paclitaxel) (N=12); Cohort 2 – First-line MSI-H/dMMR metastatic CRC treated with pela plus atezo (N=19); Cohort 3 – Third-line metastatic CRC treated with pela plus atezo and chemotherapy (trifluridine/tipiracil) (N=14); and Cohort 4 – Second-line or later advanced squamous cell carcinoma of the anal canal treated with pela plus atezo (N=10). In Cohorts 1 and 3 (chemotherapy-containing cohorts) the first 3-6 patients enrolled comprise a safety run-in. The primary objectives of GOBLET are safety and efficacy measured by the objective response rate (ORR) at week 16. Based on pre-specified response thresholds, any cohort showing a positive ORR signal in Stage 1 may advance to the 2nd Stage and enroll additional patients. The three safety run-in patients in Cohorts 1 and 3 have been enrolled and their safety data reviewed by the independent Data Safety Monitoring Board (DSMB). The DSMB identified no safety signal and recommended that enrollment into these cohort continue without modification. Enrollment into Cohorts 2 and 4 is ongoing as these cohorts do not include safety run-ins. Tumor response results to date indicate that two of the three Cohort 1 patients had a partial response at week 8, the third Cohort 1 patient had a partial response at week 16. No safety signal was observed in either the Cohort 1 (first-line pancreatic cancer) or Cohort 3 (third-line CRC) patients. This is consistent with the favorable safety profile observed in prior studies of pela in multiple cancer indications, and it supports the ability to safely treat patients with advanced GI cancers using pela in combination with checkpoint inhibitors and chemotherapy. Preliminary tumor responses to therapy in first-line pancreatic cancer patients are encouraging.

Durvalumab (D) in combination with olaparib (O) for advanced, previously treated non-small cell lung cancer (NSCLC).

e21153 Background: Poly (ADP-ribose) polymerase inhibitors (PARPi) show variable clinical activity in individuals with advanced cancers. In the lung-MAP substudy S1400G, talazoparib alone was not sufficiently active in squamous lung cancers with homologous recombinant repair deficiency. Combinations of PARPi with immune checkpoint inhibitors (ICIs) are under investigation since preclinical studies show an immunostimulatory effect of PARPi that can potentially increase responsiveness to ICIs. To test this hypothesis, we evaluated the PARPi, O with the ICI, D in individuals with advanced NSCLC who had received at least one prior platinum-based regimen. Methods: Eligible participants were enrolled in an expansion cohort of a proof-of-concept phase I/II study (NCT02484404) and received O 300 mg PO BID with D 1500 mg IV every 4 weeks until disease progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS). Results: Between July 2016 and July 2021, 15 participants with recurrent NSCLC were enrolled (median age: 66 years; stage IV: 12; adenocarcinoma 11; prior ICI: 9). After median potential follow-up of 39.6 months (mo), median PFS (mPFS) was 3.2 mo (95% CI: 0.9-7.6). Among 14 subjects with known EGFR mutation status, mPFS was longer in 11 individuals with EGFR-WT tumors (5.7 vs. 0.9 mo; p = 0.001). DNA repair mutation ( APC, BAP1, BRCA1, BRCA2, CHEK2, FANCI, FANCL and PALB2) status was known for 9 subjects; mPFS of subjects with (n = 7) or without (n = 2) DNA repair mutations was 3.2 vs. 18.1 mo (p = 0.68), respectively. Tumor PD-L1 expression > 50% (n = 3/10) and prior ICI therapy (n = 9/15) was associated with longer, albeit not statistically significant, mPFS: 7.6 vs. 1.8 mo; p = 0.22, and 5.7 vs. 1.8 mo; p = 0.39, respectively. Two (13%) partial responses, 7 (47%) stable disease and 6 (40%) cases of progressive disease were observed. Four (27%) subjects, including 3 previously treated with ICIs, achieved durable response or stability for up to 3 years. Treatment-related adverse events (TRAEs) were generally mild (grade 1 or 2). The most common TRAEs were anemia (40%), thrombocytopenia (27%), anorexia, fatigue, pain, and hypophosphatemia (each observed in 20%). Grade > 3 TRAEs occurred in 4 (27%) subjects (all hematologic). Immune-related AEs occurred in 4 (27%) individuals. Two subjects developed myelodysplasia after 12 and 36 mo of treatment. Three (20%) subjects required dose reductions or discontinuation of O due to anemia. There were no treatment-related deaths. Accrual will continue until 20 eligible participants are enrolled. Conclusions: O+D has acceptable safety and modest efficacy in an unselected population with recurrent NSCLC. Sufficient clinical activity is not observed in individuals with EGFR-mutated tumors. Genomic and immunological analyses are being performed to identify predictive biomarkers in individuals with durable benefit and will be reported. Clinical trial information: NCT02484404.

A phase II clinical trial of neoadjuvant sasanlimab and stereotactic body radiation therapy as an in situ vaccine for cisplatin-ineligible muscle invasive bladder cancer (RAD VACCINE MIBC).

TPS4611 Background: The utilization of neoadjuvant immune checkpoint inhibitor (ICI) therapy, including anti-PD1/L1 agents, prior to radical cystectomy (RC), is an emerging paradigm in muscle invasive bladder cancer (MIBC). Pathologic complete responses (pCR) have been observed in 25-40% of patients with neoadjuvant PD1/L1 inhibitor monotherapy for cisplatin-ineligible MIBC. In situ vaccination using stereotactic body radiation therapy (SBRT) may augment T-cell responses to tumor-specific antigens through immunogenic cell death. Sasanlimab (PF-06801591) is a humanized IgG monoclonal antibody that targets PD-1 selectively, for which there are both Phase 1 data and ongoing Phase 3 trials in early-stage urothelial carcinoma. There exists a strong rationale to evaluate a novel strategy of combination neoadjuvant ICI therapy with SBRT as an in situ vaccine to improve loco-regional control and decrease the risk of distant recurrence in cisplatin-ineligible patients with MIBC. Methods: This is a prospective, investigator-initiated, single-arm, single-institution, phase II trial that evaluates neoadjuvant sasanlimab in combination with SBRT as neoadjuvant therapy for patients with MIBC before RC. Eligibility requires patients to be cisplatin-ineligible (one of the following: ECOG-PS=2, creatinine clearance <60 ml/min, or comorbidities such as hearing loss or neuropathy) or those who refuse cisplatin-based chemotherapy. Sasanlimab (300 mg) will be administered subcutaneously on Day 1 of each 28-day cycle for a total of 2 cycles, in combination with SBRT to the primary tumor at a dose of 24Gy given in 3 fractions, starting on Day 1 of Cycle 2 with a 48-hour interval between fractions. The combination treatment will be assessed by using a Simon’s 2-Stage design, which the first 10 patients are enrolled as a safety lead-in to evaluate the safety and feasibility. Futility analysis will be performed after a total of 18 patients. The primary endpoint is pCR rate after neoadjuvant sasanlimab/SBRT, followed by RC. If pCR is observed in 4 or fewer patients, further enrollment of patients may be stopped with the conclusion that pT0 cannot be 40% or greater. Otherwise, an additional 15 patients will be accrued in stage II, resulting in a total of 33 patients. Secondary endpoints include adverse events, surgical complication rates, health related quality-of-life, overall survival, and recurrence free survival. Exploratory endpoints include analysis of and association with pCR of the tumor/germline genetic signatures, circulating tumor DNA, tumor PD-L1 expression, blood cytometry time-of-flight analysis to identify immune response. Enrollment opened on February 15, 2022. Clinical trial information: NCT05241340.

Toripalimab (anti-PD-1) monotherapy as a second-line treatment for patients with metastatic urothelial carcinoma (POLARIS-03): Two-year survival update and biomarker analysis.

4566 Background: Patients with advanced metastatic urothelial carcinoma (mUC) who experience disease progression after standard therapy have limited treatment options. Toripalimab was approved for the 2nd line treatment of mUC based on a phase II clinical study (POLARIS-03) in Chinese patients with mUC (NCT03113266). Here we report the two-year efficacy update and biomarker analysis of the study. Methods: Metastatic UC Patients received toripalimab 3 mg/kg Q2W until disease progression, unacceptable toxicity or voluntary withdrawal. Clinical response was assessed every 8 weeks by independent review committee (IRC) per RECIST v1.1. Tumor PD-L1 expression, tumor mutational burden (TMB), and other biomarkers were evaluated for correlation with clinical response. Results: From May 2017 to September 2019, 151 patients were enrolled from 15 participating centers. By cutoff date of September 8, 2021, no emergent of new safety signal was identified compared with the previous one-year report. By the cutoff date, 3 CR, 37 PR and 28 SD were observed among the ITT population for an ORR of 26.5% and a DCR of 45.0% as assessed by the IRC. The response was durable as the median duration of response was 25.8 months. The median OS was 14.6 months. Whole exome sequencing (WES) was performed on tumor biopsies and paired PBMCs and the results were available from 135 patients. The median TMB value was 4.1 mutations per million base pairs (Mb) in the cohort. Using 10 mutations/Mb as the cut off, TMB-high patients (n = 27) had better ORR than TMB low patients(n = 108) (48% versus 22%, p = 0.014). The TMB-high group also showed better PFS (12.9 versus 1.8 months, HR = 0.48 [95% CI:0.31-0.74], p < 0.001) and OS (not reached versus 10.0 months, HR = 0.53 [95% CI:0.32-0.88], p = 0.013) than the TMB low group. Patients with mutations in chromatin remodelers SMARCA4/PBRM1 or tumor suppressor RB1 were associated with better responses to toripalimab than patients with wild-type genes. The ORR was 30% (6/20) in patients with FGFR2/FGFR3 mutations or FGFR2/FGFR3 gene fusions, and 42% (5/12) in patients with NECTIN4 genomic alternations. The mutational signature characterized by exposure to aristolochic acid (A:T to T:A transversion) is present in both upper tract urothelial carcinoma (UTUC) and lower tract urothelial carcinoma (LTUC), but enriched in UTUC (p = 0.003). Similar clinical responses were observed in UTUC and LTUC. Conclusions: Toripalimab has demonstrated a manageable safety profile and encouraging clinical activity in metastatic UC patients refractory to 1st line chemotherapy. WES analysis identified divergent mutations in the study. We report the utility of TMB to predict not only the response rate but also the PFS and OS benefits in patients with mUC in response to an ICI monotherapy. Clinical trial information: NCT03113266.

Two cycles versus three cycles of neoadjuvant sintilimab plus platinum-doublet chemotherapy in patients with resectable non-small-cell lung cancer (neoSCORE): A randomized, single center, two-arm phase II trial.

8500 Background: Neoadjuvant immune checkpoint inhibitors (ICIs) plus chemotherapy have a promising efficacy in resectable non-small-cell lung cancer (NSCLC), yet the period of neoadjuvant immunochemotherapy is undetermined. This phase II study compared the efficacy and safety of two cycles with three cycles of neoadjuvant sintilimab plus chemotherapy in resectable stage IB-IIIA NSCLC. Methods: This randomized, open-label phase II trial recruited patients aged 18 or older with histologically confirmed, treatment-naïve, American Joint Committee on Cancer-defined stage IB-IIIA, resectable NSCLC. Eligible patients were randomly assigned to two or three cycles of neoadjuvant treatment with intravenous sintilimab (200 mg) plus carboplatin (area under curve 5) and nab-paclitaxel (260mg/m2, for squamous) or pemetrexed (500mg/m2, for non-squamous) on day 1 of three-week cycle. After surgical resection, patients received totally four doses of perioperative immunochemotherapy, followed by one-year sintilimab maintenance under patient decision. Randomisation was stratified by tumor PD-L1 expression (≥1% vs < 1%). The primary endpoint was MPR rate. Secondary endpoints included complete pathology response (pCR) rate, objective response rate (ORR), 2-year disease-free survival (DFS) rate, 2-year overall survival (OS) rate and safety. This trial is registered with ClinicalTrials.gov, number: NCT04459611. Results: From 6/2020 to 9/2021, 60 patients were enrolled and received neoadjuvant treatment. The patient characteristics of both arms were well balanced. Among 55 patients with successful R0 resection, we observed a higher MPR rate (41.4%, 12/29) in three-cycle group compared with two-cycle group (26.9%, 7/26) (p = 0.260), meanwhile, pCR rate achieved 24.1% (7/29) and 19.2% (5/26) respectively (p = 0.660). Patients of squamous subtype generally achieved a statistically higher MPR rate (51.6%, 16/31) compared with the non-squamous subtype (12.5%, 3/24) (p = 0.002). In squamous subgroup, three cycles neoadjuvant treatment induced a MPR rate of 60% compared with 43.8% after two cycles treatment (p = 0.366).In the meantime, the MPR rate was 21.4% versus 0% in non-squamous subgroup, respectively (p = 0.239). The ORR showed no statistical difference between three-cycle group (55.2%, 16/29) and two-cycle (50%, 13/26) (p = 0.701). Patients were well-tolerated in both groups and 5% (3/60) experienced grade 3 immune related adverse events. Conclusions: It is the first randomized study comparing different treatment periods of immuno-chemotherapy in the neoadjuvant setting. Three cycles neoadjuvant treatment achieved a numerically higher MPR rate compared with two cycles. Patients with squamous lung cancer obtained a better MPR rate compared with non-squamous subtype. Clinical trial information: NCT04459611.

A phase II trial evaluating combination pemetrexed and avelumab in patients with MTAP-deficient advanced urothelial cancer.

TPS4612 Background: MTAP-deficiency occurs primarily due to homozygous loss in chromosome 9p21 and is seen in approximately 25% of urothelial cancers. MTAP-deficiency portends aggressive biology with poorer outcomes than in MTAP-proficient tumors; for example, in the IMvigor210 data, MTAP-deficient patients had median overall survival of 8.0 months, compared to 11.3 months in MTAP-proficient patients (p = 0.042). MTAP-deficient tumors lack salvage nucleotide synthesis pathways and thus are uniquely sensitive to anti-folate agents; however, in prior clinical work with pemetrexed in these tumors, responses are relatively short-lived. In-vivo data has suggested that pemetrexed can increase tumor infiltrating T-cells, macrophages, dendritic cells, and PD-L1 expression in MTAP-deficient tumors and decrease myeloid-derived suppressor cells (MDSCs). As such, it was postulated that sequential treatment with anti-folate chemotherapy (pemetrexed) and immune checkpoint inhibition (avelumab) would improve responses in MTAP-deficient urothelial cancer. Methods: A prospective phase II trial of patients with advanced MTAP-deficient urothelial cancer is being conducted under IRB-approved protocol NCT03744793. This study will enroll 25 patients at a single site (The University of TX, MD Anderson Cancer Center). Key eligibility criteria include patients with advanced MTAP-deficient urothelial cancer with measurable disease in second-line or beyond. MTAP-deficiency is confirmed with CLIA-approved IHC or NGS. Patients are stratified as being IO-pretreated versus IO-naïve. All patients receive a lead-in cycle of pemetrexed (500 mg/m2) followed by combination pemetrexed (500 mg/m2) and avelumab (10 mg/kg) IV every three weeks until disease progression, patient withdrawal, or unacceptable toxicity. Three biopsies per patient with tissue collection at trial baseline, on single agent pemetrexed, and on combination pemetrexed-avelumab are performed. The primary objective of this trial is to evaluate response rate with sequential pemetrexed and avelumab in MTAP-deficient urothelial cancer. Imaging response assessment is done via RECIST v1.1. Secondary objectives are to evaluate progression-free survival (PFS) and overall survival (OS), as well as to perform correlative studies evaluating the effect of this therapy on immune cells and tumor microenvironment. This correlative work includes but is not limited to evaluation of peripheral T-cells, tumor-infiltrating T-cells, macrophages, and MDSCs. Interim analyses for futility and safety occur in cohorts of 5 patients and are performed based on Bayesian sequential methods. Fifteen patients have been enrolled thus far. Clinical trial information: NCT03744793.

CD3D Is an Independent Prognostic Factor and Correlates With Immune Infiltration in Gastric Cancer.

The protein encoded by CD3D is part of the T-cell receptor/CD3 complex (TCR/CD3 complex) and is involved in T-cell development and signal transduction. Previous studies have shown that CD3D is associated with prognosis and treatment response in breast, colorectal, and liver cancer. However, the expression and clinical significance of CD3D in gastric cancer are not clear. In this study, we collected 488 gastric cancer tissues and 430 paired adjacent tissues to perform tissue microarrays (TMAs). Then, immunohistochemical staining of CD3D, CD3, CD4, CD8 and PD-L1 was conducted to investigate the expression of CD3D in gastric cancer and the correlation between the expression of CD3D and tumor infiltrating lymphocytes (TILs) and PD-L1. The results showed that CD3D was highly expressed in gastric cancer tissues compared with paracancerous tissues (P<0.000). Univariate and multivariate analyses showed that CD3D was an independent good prognostic factor for gastric cancer (P=0.004, HR=0.677, 95%CI: 0.510-0.898 for univariate analyses; P=0.046, HR=0.687, 95%CI: 0.474-0.994 for multivariate analyses). In addition, CD3D was negatively correlated with the tumor location, Borrmann type and distant metastasis (P=0.012 for tumor location; P=0.007 for Borrmann type; P=0.027 for distant metastasis). In addition, the expression of CD3D was highly positively correlated with the expression of CD3, CD4, CD8, and PD-L1, and the combination of CD3D with CD3, CD4, CD8 and PD-L1 predicted the best prognosis (P=0.043). In summary, CD3D may play an important regulatory role in the tumor immune microenvironment of gastric cancer and may serve as a potential indicator of prognosis and immunotherapy response.

P19 Loss of heterozygosity associates with PD-L1 expression and tumor mutational burden in high-grade endometrial tumors

P19 Loss of heterozygosity associates with PD-L1 expression and tumor mutational burden in high-grade endometrial tumors

PD-L1 expression and microsatellite instability in tumors of unknown primary site.

2635 Background: Cancer of unknown primary site is a heterogeneous group of tumors for which the origin remains unknown, despite detailed investigation. Its clinical presentation occurs due to symptoms resulting from metastasis, which can be influenced not only by biological processes of the tumor, but also due to regulatory processes in the tumor microenvironment such as PD-L1. Microsatellite instability (MSI) is a predictive biomarker for cancer immunotherapy and its status as well as co-occurrence with PD-L1 expression is poorly evaluated. The aim of this study was to evaluate the expression of PD-L1 and the status of MSI in tumors of unknown primary site and their possible associations with clinical-pathological characteristics and clinical outcomes in patients with this type of tumor. Methods: The PD-L1 expression was evaluated using the immunohistochemistry technique and measured by CPS and TPS scores. MSI status was assessed using a hexa-plex marker panel by polymerase chain reaction followed by fragment analysis. Overall survival was analyzed using the Kaplan Meier method and comparisons of the curves using the log rank test. Results: Of the 121 conclusive cases for MSI status, only two cases (1,6%) were MSI-High. PD-L1 expression, assessed by both TPS and CPS, was positive in approximately 18% of 108 conclusive cases. PD-L1 expression is significantly less frequent in patients with a predominance of hepatic or bone metastasis and more frequent in patients with a predominance of nodal metastasis. The median overall survival was about 4 months, and the predominance of liver metastases was associated with a worse prognosis, while the use of chemotherapy and low ECOG-PS were associated with better survival. PD-L1 expression was associated with better overall survival. Conclusions: PD-L1 is expressed in a subset of patients with cancer of unknown primary site, while MSI is a rare event. It is necessary to better explore the microenvironment of this type of tumor as well as the role of immunotherapy to change such a dismal clinical outcome.

The predictive values of POTEE mutations for response to immune checkpoint inhibitors in lung adenocarcinoma.

e21110 Background: Precise selection of patients who could benefit from immune checkpoint inhibitors (ICIs)is an important challenge for immunotherapy in lung cancer. POTEE is a member of one primate-specific gene family which have been identified as cancer-related antigens and potential target for immunotherapy of cancer. Here, we investigated the correlation between POTEE mutation and the clinical outcomes of ICIs treatment in lung adenocarcinoma (LUAD). Methods: We merged three independent cohorts from publicly accessible data, the Miao(n = 47), Rizvi (n = 29) and Hellmann (n = 59), to explore the associations between POTEE mutations ( POTEE-mut) and ICIs efficacy. Then we explored the relationship between POTEE mutation and tumor mutational burden (TMB) and PD-L1 expression in the merged cohort. Further, gene set enrichment analyses (GSEA) was used to explore the potential molecular mechanism in The Cancer Genome Atlas (TCGA)-LUAD cohort. Results: In merged cohort, the mutation frequency of POTEE was 7.41% (10 in 135). POTEE-mut group had a significantly higher objective response rate (ORR) (100% vs 27.2%; Fisher’s exact test; P &lt; 0.001) compared to POTEE wildtype group. Kaplan-Meier analysis revealed that POTEE-mut was significantly associated with longer progression-free survival (PFS) (not reached vs 6.1 months, P = 0.001). And at multivariable analysis adjusted by cohort, age, smoking status, line of immunotherapy, PD-L1 expression and TMB, POTEE-mut group showed significant improved PFS with a HR of 0.09(95% CI 0.01-0.71, P = 0.022). Then we explored the association of POTEE alterations with TMB and PD-L1 expression. In merged cohort significantly higher TMB were found in LUAD patient with POTEE mutation (Mann-Whitney U test; p &lt; 0.001). However, there was no association between POTEE mutation and PD-L1 expression. We further explored the potential mechanism of POTTE mutation affecting immunotherapy response using TCGA-LUAD data. GSEA analysis revealed prominent enrichment of signatures related to DNA repair in patients with POTEE mutation (P &lt; 0.001). In detail, four DNA damage response (DDR) pathways, homologous recombination repair (HRR) (NES = 2.108, P &lt; 0.001), translesion DNA synthesis (NES = 1.587, P = 0.01), checkpoint factors (NES = 1.865, P &lt; 0.001) and base excision repair (NES = 1.737, P = 0.002), were all significantly enriched in POTEE-mut tumor. Conclusions: Our data indicated that POTEE mutations were associated with the better response for immunotherapy of LUAD, implying that it can be used as a biomarker for predicting the efficacy of LUAD immunotherapy. POTEE mutation was associated with higher TMB and changed the activity of DNA repair related pathways in LUAD. These may be the underlying mechanisms for POTEE mutations to affect the prognosis of immunotherapy.

Comparative analysis of microsatellite instability-high (MSI-H) BRAF V600E-mutated versus MSI-H BRAFwild type colorectal cancers (CRC), including tumor microenvironment (TME), associated genomic alterations, and immunometabolomic biomarkers.

3066 Background: The BRAFV600E mutation is associated with the hypermethylator phenotype CIMP, which can also lead to the MSI-H phenotype. BRAFV600E mutation and MSI-H/dMMR status seem to be biologically intertwined; however, the impact of coexisting BRAFV600E mutations on the TME and immunometabolomic features of MSI-H/dMMR CRC tumors is not well characterized. Methods: A retrospective review of deidentified records of patients with MSI-H/dMMR CRC tumors was conducted using next-generation sequencing data (Tempus |xT assay: DNA-seq of 595-648 genes at 500x coverage, and full transcriptome RNA-seq). Several immune markers of tumor immunogenicity in BRAF wild-type ( BRAFwt) vs. V600E-mutated (BRAFV600E) tumors were assessed, including tumor mutational burden (TMB), neoantigen tumor burden (NTB, ScanNeo), PD-L1 expression, immune infiltration, and canonical immuno-metabolomic pathways (82 geneset signatures). Results: A total of 459 MSI-H/dMMR CRC tumors were analyzed, of which 123 (27%) tumors harbored BRAFV600Emutations, and 336 (73%) were BRAFwt. MSI-H/dMMR BRAFV600E tumors were more frequently identified in females (69% vs. 55%; P= 0.01), non-Hispanic or non-Latino (100% vs. 73%; P =0.001), and older patients (median age: 76 yrs vs. 62 yrs; P&lt; 0.001). Compared to BRAFWT, BRAFV600E tumors exhibited significantly higher TMB (Median: 49 mut/MB vs. 36 mut/MB; P &lt; 0.001) and were more frequently associated with TMB-High status (&gt; 10 mut/MB; 100% vs. 95%; P = 0.008); however, no significant differences were observed with tumor NTB, immune score, or T cell infiltration (CD4 or CD8). NK cell infiltration was higher in the BRAFV600Ecohort (&lt; 0.001). When compared to BRAFWT tumors , BRAFV600E tumors harbored a greater frequency of mutations in MSH6(42% vs. 20%), B2M (33% vs. 16%), BRCA2 (31% vs. 12%), ATM (23% vs. 12%), and TP53 (30% vs. 19%) but a lower frequency of MSH2 (3.3% vs. 11%), all P&lt; 0.05. Pathway enrichment analysis identified 10 significantly altered signaling pathways, most of which related to stromal/immune cell signaling and metabolism. Five were upregulated among BRAFV600E tumors: glycerophospholipid, galactose, cyclin-dependent cell signaling; Nucleotide, and TH1 inflammation. Five pathways were downregulated (Wnt, Notch, TH17 inflammation, amino sugar, and cancer stem cell signaling). Conclusions: MSI-H/dMMR BRAFV600E CRCs undergo broad metabolic reprogramming (e.g., glycerophospholipidgalactose, nucleotide). A rise in lipid metabolism, particularly with NK inflammation, suggests that BRAFV600Emutated tumors may be associated with a non-classical immune component. BRAFV600E and BRAFwt CRCs exhibited similar NTB and T cell infiltration, suggesting that both are likely to benefit from immune checkpoint inhibitors.

Impact of RAS mutations on immunologic characteristics of the tumor microenvironment (TME) in patients with microsatellite instability-high (MSI-H) or mismatch-repair–deficient (dMMR) colorectal cancer (CRC).

3067 Background: The KEYNOTE-177 trial demonstrated pembrolizumab’s superiority over first-line chemotherapy in patients with MSI-H/dMMR mCRC. However, in a subgroup analysis, patients with KRAS or NRAS mutations did not show the same favorable PFS benefit with PD-1 blockade therapy (HR 1,19; CI 0.68-2,07). The impact of RAS mutations on the immunologic characteristics of the TME of MSI-H/dMMR CRC has not been well characterized. Methods: A retrospective review of deidentified records of patients with MSI-H/dMMR CRC tumors was conducted using next-generation sequencing data (Tempus |xT assay, DNA-seq of 595-648 genes at 500x coverage, and full transcriptome RNA-seq). MSI-H determined by assessment of 239 loci by NGS. Several immune markers were assessed, including tumor mutational burden (TMB), neoantigen tumor burden (NTB, ScanNeo), PD-L1 expression, immune infiltration, and canonical immune pathways (82 geneset signatures). Results: A total of 463 MSI-H/dMMR CRCs were analyzed, of which 110 (24%) tumors harbored RAS mutations ( RASmut) [ KRAS: 93%, NRAS 6% and HRAS 1%}, while 353 were RAS-wild-type ( RASWT). Compared to MSI-H/dMMR RASWT, MSI-H/dMMR RASmut tumors were more frequently identified in males (53% vs. 38%; P= 0.005), and younger patients (median age: 57 yrs vs. 71 yrs, P&lt; 0.001). Although there were no significant differences in median TMB (40 mut/MB for both, p = 0.9) or frequency of TMB-high status (≥10 mut/MB) between the two groups, RASmuttumors tended to have a lower tumor NTB (16 vs. 12 neoAg/Mb, P &lt;0.001) and lower % CD8 T cell but higher % CD4 T cell infiltration (P &lt; 0.05). Significant differences were observed in genomic alterations co-occurring with RASmut compared to RASWT (e.g., MLH1 (23% vs. 8.8%, P &lt; 0.001), MSH6 (36% vs. 24%, P = 0.017), APC (60% vs. 20%, P&lt; 0.001), ARID1A (54% vs 30%, P&lt; 0.001), PIK3CA (36% vs 19%, P&lt; 0.001), and TP53 (32% vs. 19%, P = 0.014). Pathway enrichment analysis identified 14 differentially expressed pathways among RASmut tumors. Four pathways showed significant upregulation, including Hedgehog, Wnt, TGFβ, and cancer stem cell pathways. Ten pathways of interest showed significant downregulation among RASmut tumors. The majority (9/10) were immune-related, including cytokine signaling [ JAK-STAT, TGFβ, TH1], innate immune [ NK cells], and adaptive immune events (CD8 T cell, Tregs)]. Conclusions: MSI-H/dMMR CRCs harboring RASmut exhibited overall upregulated WNT/SHH pathway activity, coupled with reduced NTB, cytokine signaling, and innate and adaptive immune events. TGFβ is pleiotropic, and different members were associated with variable modulation. These data suggest that MSI-H/dMMR CRCs harboring RAS mutations are less immunogenic and appeared to contain a TME that is less sensitive to immune checkpoint blockade than MSI-H/dMMR RAS wt CRCs.

The correlation between tumor mutation burden and TP53 or CHEK2 germline mutations in malignant tumors.

e22527 Background: Li-Fraumeni syndrome (LFS) is a rare autosomal dominant cancer predisposition syndrome, mainly caused by the lack of tumor suppressor gene TP53. The LFS related tumors include breast cancer, brain tumors, malignant sarcoma, bone cancer and central nervous system tumors. In addition to TP53 germline mutations, studies have shown that CHEK2 is also a susceptibility gene for LFS, and CHEK2 germline mutations is related to a series of cancer types. However, the correlation between tumor mutation burden (TMB), age, gender, PD-L1 expression and TP53 or CHEK2 germline mutations in malignant tumors remains unknown. Methods: In this study, we retrospectively analyzed the mutation characteristics of TP53 or CHEK2 germline mutations in patients with solid tumors without selecting age or family history. We identified 631 patients harboring TP53 or CHEK2 mutations from 9337 patients with malignant solid tumors. According to the ACMG (American College of Medical Genetics and Genomics) guidelines in pathogenicity, the 631 patients in the retrospective cohort were divided into three groups, including P/LP group (with pathogenic or likely-pathogenic mutations), VUS group (with uncertain significance mutations) and B/LB group (with benign or likely-benign mutations). We also analyzed the differences in TMB, age, gender and PD-L1 expression among the three groups. Statistical significance was defined as P-value less than 0.05. Results: The 631 (631/9337) patients carried TP53 or CHEK2 germline mutations were identified, in which 33 patients with pathogenic mutations and 15 patients with likely-pathogenic mutations. These pathogenic or likely-pathogenic mutations mainly occurred in lung cancer, brain tumors, colorectal cancer and liver cancer, accounting for about 35.4%, 20.8%, 16.7% and 12.5%, respectively. Among the three groups, TMB was significantly different between P/LP group and B/LB group (P = 0.037), and the B/LB group was higher. In addition, we found that the three groups had no significant differences in age, gender and PD-L1 expression. Conclusions: Our data showed that 0.823% (48/8535) malignant solid tumor patients carried TP53 (28/48) or CHEK2 (20/48) germline pathogenic or likely_ pathogenic mutations. In addition, the TMB value in B/LB group was significantly higher than that in P/LP group. The other characteristics of LFS will be studied in the future.

Phase Ib INEOV neoadjuvant trial of durvalumab +/- tremelimumab with platinum chemotherapy for patients (pts) with unresectable ovarian cancer (OC): Final complete resection and pathological response rates.

5557 Background: We have shown that neoadjuvant carboplatin and paclitaxel (NACP) increased tumor infiltrating lymphocytes and PDL1 expression in OC pts. INEOV evaluated NACP with durvalumab (D) +/- tremelimumab (T) in pts with unresectable OC. We previously reported that NACP with D+/-T was feasible and safe but the addition of T did not improve interval debulking surgery (IDS) rates after 3 cycles (C3) (ESMO 2021). Here we provide an update with longer follow up including data on delayed IDS performed after 6 cycles of neoadjuvant treatment. Key secondary endpoints include complete resection (CC0) and complete pathological response rates. Methods: Pts with stage IIIC/IV OC were randomized to NACP + D (1125mg) alone (arm A) or with T (75mg once at C2) (arm B). Interval debulking surgery (IDS) was planned after C3, or delayed after C6. Pts in arm A not operable after C3 crossed over to arm B, pts in arm B crossed over to standard of care (SOC). Pts were assessed for delayed IDS after C6. Complete pathological response (pCR) was defined as no residual tumor cells found on any surgical specimens, or no residual tumor cells on any samples outside the ovary at IDS. Results: Sixty four (N = 64) of 66 pts (IIIC/IV: 70%/30%) randomized were evaluable. After C3, 66% (21/32) of pts in arm A and 59% (19/32) in arm B had IDS. The 11 pts in arm A not candidate for IDS after C3 crossed over to arm B until C6 and 5/11 benefited from delayed IDS. The 13 pts in arm B inoperable at C3 went on to receive SOC (NACP +/- bevacizumab), and 5/13 became eligible for delayed IDS after C6. Overall, IDS was performed in 50 of 64 evaluable pts, and most (45/50) achieved macroscopically complete resection (CC0), so that the overall CC0 rate was 70% (45/64), with no significant difference between arms (CC0 = 75% vs 65% in arm A vs B). Among the 50 pts who had IDS, complete pathological responses were observed in 18% of pts. Conclusions: Taking into account the whole treatment strategy including delayed IDS after 6 cycles of neoadjuvant treatment, we have shown that neoadjuvant CP with D+/- T results in encouraging CC0 (70%) and pCR (18%) rates. However there was no apparent benefit to the addition of T to D. Studies are ongoing to describe the immune features predictive of pCR as well as the impact of treatment on the immune microenvironment. Clinical trial information: NCT03249142.

Outcomes of single-agent PD-(L)-1 versus combination with chemotherapy in patients with PD-L1-high (≥ 50%) lung cancer.

9052 Background: Single agent PD-(L)-1 blockade (IO) and PD-(L)-1 blockade combined with chemotherapy (ChemoIO) are both standard first-line treatments for patients with PD-L1-high (≥ 50%) metastatic non-small cell lung cancer (NSCLC). These regimens have not been compared prospectively, so comparative effectiveness is unclear. It is also unknown if clinical and molecular tumor characteristics differentially associate with benefit to IO vs ChemoIO in patients with NSCLC with high PD-L1 tumor expression. Methods: All patients with metastatic NSCLC treated with IO or ChemoIO at two institutions (Memorial Sloan Kettering Cancer Center and Dana-Farber Cancer Institute) were reviewed. Patients with EGFR or ALK alterations, PD-L1 expression &lt; 50%, treated with IO or ChemoIO in &gt; 1st line setting were excluded. Overall survival (OS), progression-free survival (PFS), and objective response rate (ORR) were compared between the IO vs ChemoIO groups and association with clinical, pathologic, and molecular features was examined. To account for NGS panel differences, tumor mutational burden (TMB) values were harmonized using a z-score conversion as previously described (Vokes et al, 2019). Results: Of 639 patients with stage IV EGFR/ ALK wild-type NSCLC and PD-L1 ≥50% treated in the 1st line setting, 504 received IO and 135 received ChemoIO. Baseline ECOG performance status (p = 0.3), median PD-L1 % (p &gt; 0.9) and TMB (p = 0.2) were similar between the IO and ChemoIO groups. For patients receiving IO vs ChemoIO, there was no significant difference in OS (HR 0.8, 95% CI 0.6 to 1.08; p = 0.2). Median PFS was shorter (HR 0.7, 95% CI 0.6 to 0.9; p = 0.004) and ORR was lower (40% IO vs 55% ChemoIO, p = 0.002) in the IO group. Among patients with durable responses (&gt; 6 months), never smokers were less common in the IO group (6% vs 18%, p &lt; 0.001), but there was no difference in PD-L1 expression, TMB, or mutational ( KRAS, STK11, or KEAP1) profile to suggest differential predictors of benefit to IO or ChemoIO. Conclusions: In patients with PD-L1 high NSCLC, there was no survival benefit associated with the addition of chemotherapy to IO. There were also no clear differences in PD-L1 expression or molecular features associated with durable response to IO vs ChemoIO. These findings have implications for treatment selection in this population.

Effect of durvalumab in patients with unresectable stage 3 non–small cell lung cancer post-chemoradiotherapy.

8550 Background: The PACIFIC study (PS) concluded that the use of durvalumab from 1 to 42 days after concurrent chemoradiotherapy (CXRT) in stage 3 unresectable non-small cell lung cancer (NSCLC) increased the median overall survival (mOS) from 29 to 48 months. It also showed a benefit in tumors with PD-L1 &lt;25%. However, a post-hoc analysis of the PS showed no survival benefit with durvalumab in patients with PD-L1 &lt;1% but was not statistically powered. Currently in the US, durvalumab is approved irrespective of PDL-1 percentage, whereas in Europe it is not approved for tumors with PDL-1 &lt;1%. Also, there was no survival benefit in starting durvalumab within and after 2 weeks of CXRT. Our objectives in this study are to analyze the impact of PDL-1 expression and the date of initiation of durvalumab post CXRT on mOS. Methods: We conducted a retrospective observational study of stage 3 unresectable NSCLC patients who received durvalumab post CXRT at LSU Health Shreveport from 2018 to 2021. A survival analysis was done including the following variables: age, race, sex, tumor histology, tumor PD-L1 percentage, and date of initiation of durvalumab post CXRT. P-value &lt;0.05 was considered statistically significant. Results: We identified 83 patients who received durvalumab after CXRT for treatment of stage 3 unresectable NSCLC. Baseline characteristics are provided in table 1. Among all the tumors, 25% had a PDL-1 &lt;1%. 33% of the study population received durvalumab less than 30 days after CXRT and 67% received it after 30 days. The mOS was not impacted by race, sex, or tumor hisotology. Compared to higher PDL-1 percentage, patients with PD-L1 &lt;1% had a statistically significant lower survival probability. At 14 months, 87% of patients with a PD-L1 &lt;1% were alive compared to 100% in those with a PD-L1 1-50% or a PD-L1 &gt;50%. Less than 35% of patients with PD-L1 &lt;1% survived beyond 30 months compared to 45% for PD-L1 1-50% and 100% for PD-L1 &gt;50% (p-value 0.02). Patients who received durvalumab 30-60 days after concurrent CXRT had a lower OS at 30 months compared to those who started before 30 days (44% versus 90%). However, statistical significance was not reached (p-value 0.45). Conclusions: This study demonstrates that patients with a PD-L1 tumor expression of &lt;1% had a statistically significant lower survival probability compared to those with a PD-L1 expression of 1-50% and &gt; 50% in this patient population. Time from CXRT to the start of durvalumab was not shown to affect survival outcomes.[Table: see text]

Final progression-free survival, interim overall survival, and biomarker analyses of CHOICE-01: A phase 3 study of toripalimab versus placebo in combination with first-line chemotherapy for advanced NSCLC without EGFR/ALK mutations.

9028 Background: Toripalimab (anti-PD-1) in combination with chemotherapy showed significant improvement in progression-free survival (PFS) and overall survival (OS) in the first-line treatment of advanced NSCLC regardless of tumor PD-L1 expression. Whole exome sequencing (WES) was performed to identify correlative biomarkers for survival. Methods: Patients (n = 465) with treatment-naïve, advanced NSCLC without EGFR/ALK mutations were randomized 2:1 to receive toripalimab 240 mg (n = 309) or placebo (n = 156) in combination with chemotherapy for 4-6 cycles, followed by maintenance of toripalimab or placebo plus standard care until disease progression, intolerable toxicity, or completion of 2 years of treatment. Stratification factors included PD-L1 expression status, histology, and smoking status. The primary endpoint was PFS by investigator per RECIST v1.1. Secondary endpoints included PFS by a blinded independent review committee (BIRC), OS and safety. Results: At the prespecified final PFS analysis (cutoff date Oct 31, 2021), a significant improvement in PFS as assessed by investigator was observed for the toripalimab arm over the placebo arm: HR = 0.49 (95% CI: 0.39-0.61), two-sided p &lt; 0.0001, median PFS 8.4 vs 5.6 months. The 1-year PFS rates were 36.7% vs 17.2%. PFS as assessed by BIRC was also significantly longer in the toripalimab arm. The improvements of PFS were observed across key subgroups, including histology and PD-L1 expression. At the interim OS analysis, the toripalimab arm had a significantly longer OS than the placebo arm: HR = 0.69 (95% CI: 0.52-0.92), two-sided p = 0.0099, median OS not reached vs 17.1 months. The incidence of Grade ≥3 adverse events (AEs) (78.6% vs 82.1%) was similar between the two arms. AEs leading to discontinuation of toripalimab/placebo (14.3% vs 3.2%) and fatal AEs (5.5% vs 2.6%) were more frequent in the toripalimab arm. WES results from 394 available patients revealed that patients with high tumor mutational burden (TMB) (≥10 mutations per million base pairs) were associated with significantly better PFS in the toripalimab arm over the placebo arm (median PFS 13.1 vs 5.5 months) (interaction P = 0.026). In addition, patients with mutations in the FAK-PI3K-Akt pathway or IL-7 signaling pathways achieved significantly better PFS and OS from the toripalimab chemotherapy combination (interaction P values ≤ 0.01). Conclusions: The addition of toripalimab to chemotherapy in patients with advanced NSCLC provided superior PFS and OS when compared to chemotherapy alone with a manageable safety profile. These results support the use of toripalimab with chemotherapy as 1st line therapy for advanced NSCLC patients without EGFR/ALK mutations. Clinical trial information: NCT03856411.

Updated results from the skin cancer cohorts from an ongoing phase 1/2 multicohort study of RP1, an enhanced potency oncolytic HSV, combined with nivolumab (IGNYTE).

9553 Background: RP1 is an enhanced potency oncolytic version of HSV1 that expresses human GM-CSF and the fusogenic protein GALV-GP R-. IGNYTE is a multicohort phase 1/2 study that evaluates the safety and efficacy of RP1 in combination with nivo (NCT03767348) in a range of tumor types. Preliminary data demonstrated a durable anti-tumor activity and tolerability for RP1+nivo. Here, we present updated results from the initial and melanoma (mel) and anti-PD1 naïve non-melanoma skin cancer (NMSC) cohorts with RP1+nivo. Methods: RP1 is administered via intratumoral injection Q2W, up to 10 mL/visit, first alone at a dose of 106 PFU/mL and then starting with the 2nd dose at 107 PFU/mL in combination with nivo (240 mg IV Q2W for 4 months (mos) then 480 mg IV Q4W up to 2 yrs) for up to 8 doses, with the option to re-initiate RP-1. Eligible patients (pts) must have at least one measurable &amp; injectable tumor of ≥ 1 cm, ECOG 0-1, and no prior oncolytic therapy. For mel, both anti-PD1 naïve and failed pts were eligible, for NMSC pts who were anti-PD1 naïve. Results: As of data extraction on January 31, 2022, 13/36 pts with mel (36.1%) and 19/31 pts with NMSC (61.3%) had a best response of PR or CR. For mel this was 5/8 (62.5%), 6/16 (37.5%), 0/6 and 2/6 (33.3%) for pts with anti-PD1 naïve cutaneous, anti-PD1/anti-PD1+anti-CTLA-4 failed cutaneous, uveal and mucosal mel respectively. For the anti-PD1 naïve NMSC this included 11/17 (64.7%), 1/4 (25%), 3/4 (75%) and 4/6 (66.6%) patients with CSCC, BCC, MCC and angiosarcoma respectively, including 8/17 (47.1%) being CR for CSCC. Current immature median DOR was 13.27 mos (current range 3.67-16.93 mos) for mel, and 7.32 mos (current range 1.88-23.11mos) for anti-PD1 naïve NMSC. Any grade TEAE ( &gt; 25%) in all cohorts combined were fatigue, nausea, pyrexia, chills, diarrhoea, pruritus, and influenza-like illness. TEAE ≥grade 3 ( &gt; 5%) were disease progression and fatigue. No deaths related to RP1 was observed, with one death related to nivo (myocarditis). Biomarker data from paired biopsies indicated robust T cell infiltration and an increase in tumor inflammation gene signature post-treatment. Clinical responses observed were independent of baseline tumor PD-L1 expression status. Conclusions: RP1 in combination with nivo provides a durable anti-tumor activity in pts with skin cancers, including anti-PD1 failed and anti-PD1/anti-CTLA-4 failed mel. The combination continued to be generally well tolerated with no new safety signals identified. Based on this data, enrollment into both a registration-directed cohort of pts who have anti-PD1 failed cutaneous mel (n = 125) and a cohort of pts with anti-PD1 failed NMSC (n = 30) is ongoing. Up-to-date data from this ongoing trial will be reported at the conference. A randomized Ph2 trial of RP1+cemiplimab vs. cemiplimab alone in anti-PD1 naïve NMSC is also underway (NCT04050436). Clinical trial information: NCT03767348.